Preferential water flow in a glacial till soil

Measured and simulated response of runoff during snowmelt has suggested that preferential water flow occurs as part of the infiltration process in glacial till. However, only a few quantitative studies have been presented. TDR measurements of soil water content were performed during the growing period in a till slope (7–10%) outside Stockholm. Soil cores were used to determine the water retention curve and the saturated hydraulic conductivity. A physically based one-dimensional model was used to simulate soil water dynamics in the slope. Two simulation approaches were used: a strict one-domain Darcian approach and a two-domain approach accounting for a bypass of the matrix flow system. The measured response of soil water content occurred within the first few hours after rainfall. This was best represented by the two-domain approach, while the response for the one-domain approach was significantly delayed with time and depth. The general behaviour of the soil water content throughout the season was, however, best simulated with a one-domain approach. The results indicated that preferential flow patterns through the unsaturated zone does not need to be considered to describe the seasonal pattern in glacial till soil. However, the results also point out that the purpose of the simulation is decisive when choosing a simulation approach, depending on whether the general soil water content over the season or the instant behaviour immediately after rainfall is of major interest.